1. Field of the Invention
The present invention relates to a body-insertable apparatus which is inserted into a subject to take an image of an examined site and to output the image by radio to an outside of the subject.
2. Description of the Related Art
In recent years, a swallowable capsule endoscope has been developed in the field of endoscope. The capsule endoscope is equipped with an imaging function and a radio function as described in Japanese Patent Application Laid-Open No. 2003-19111, for example. After being swallowed from the mouth of a patient for an observation of an interior of a body cavity, the capsule endoscope travels through internal organs such as an esophagus, a stomach, and a small intestine, following peristaltic movements thereof to sequentially perform imaging until naturally excreted from the body of the patient.
While the capsule endoscope travels through the body cavities, image data obtained through imaging by the capsule endoscope inside the body cavities is sequentially transmitted by radio communication to the outside of the patient (in other words, subject) from an antenna such as a coil antenna. The antenna is arranged at the center of a back-end side of the capsule endoscope which is an opposite side from a side where an illuminating unit and an imaging unit are arranged. The transmitted image data is stored in a memory provided inside a receiver outside the subject. A doctor or a nurse can make diagnosis based on an image shown on a display according to the image data stored in the memory.
Conventionally, commonly-used capsule endoscopes of the above-described type are monocular capsule endoscopes. The monocular capsule endoscope takes only the image of an examined site located in front of the capsule endoscope, i.e., in an advancing direction thereof. In recent years, however, a pantoscopic capsule endoscope has been proposed for widening the field of view at the time of observation of, for example, an esophagus. The pantoscopic capsule endoscope takes images of a site behind itself as well as a site in front of itself along the advancing direction. As described in US Patent Application Laid-Open No. 2002-109774, for example, the pantoscopic capsule endoscope is configured to take images behind as well as ahead of a capsule-like casing along the advancing direction thereof in the body cavities, and a set of an illuminating unit such as a light emitting diode (LED) which illuminates an examined site and an imaging unit such as a charge-coupled device (CCD) which takes an image of an examined site is arranged in the capsule-like casing, one set at each of a front-end side and a back-end side.
In the pantoscopic capsule endoscope, one set of the illuminating unit and the imaging unit is arranged at each of the two ends of the capsule-like casing, and therefore, the antenna cannot be arranged at one end side of the capsule-like casing as in the monocular capsule endoscope. Therefore, the antenna must be arranged between or around components housed inside the capsule-like casing (for an example of the monocular capsule endoscope, see Japanese Patent Application Laid-Open No. 2001-112740, for example).
In the capsule-like casing, however, various components are housed, such as a substrate on which a conductive pattern, in particular, a wide ground pattern for grounding is formed, for example, and many electronic components mainly of metal. Therefore, when the antenna is arranged between or around the housed components, transmission waves from the antenna tend to be negatively affected, for example, distorted, shielded, or absorbed, by the conductor or metals. Then, it is difficult to obtain a desirable antenna characteristic, such as a wide directionality. Further, the arrangement of the antenna between or around the housed components necessitates the increased size of the capsule-like casing. Such necessity contradicts a demand for downsizing.
Further, even in the monocular capsule endoscope, the coil antenna, for example, is usually arranged at the center of the back-end side of the capsule-like casing and occupies a large space, and hampers a further downsizing of the capsule-like casing.